US-A-2009/0107597 describes a tire with a wear resistant rubber tread having a cap/base construction. At the lateral edges of the tread and adjacent to the tire shoulders, the tread base layer extends to the tread running surface. The tread cap rubber compound and the tread base rubber compound may comprise silica. The axial width of the extensions of the tread base layer at the tread running surface is at least 20 mm. A similar tire construction is also known from DE-C-198 12 934 and EP-B-0 798 142.
U.S. Pat. No. 6,415,833 describes a tire having a tread, the tread comprising one or two strips of an electrically good conducting, silica-free rubber composition extending in radial direction from the tread running surface through the tread. The strips have an axial width in a range of from 0.1 to 1 mm.
U.S. Pat. No. 5,942,069 describes a tire having a tread having a cap/base construction. The base extends in one or more strips from the tread base layer radially outside to the tread running surface. The rubber compound of the tread base layer is an electrically good conducting, silica-free rubber composition.
U.S. Pat. No. 4,478,266 describes a composite tread compound having a radially outer low hysteresis compound and a radially inner high hysteresis compound. Both compounds are free of silica. The inner compound extends in a triangular pattern radially outwards into the outer compound.